Electrical disconnector

ABSTRACT

A disconnector for lightning arresters is provided with a simplified configuration wherein a cup-shaped breakable housing has within it a substantially concentric insulating support member that is recessed to accommodate an explosive containing metal case resting on an end portion of a ground terminal. The insulating support defines a fixed spark gap spacing between the metal case and an electrode making direct contact with a lightning arrester. A flexible grading resistor is provided in parallel with the spark gap and comprises a flexible insulating core on which is wound a plurality of turns of resistive wire, the resistor encircling the insulating support in the space between it and the inner housing wall.

United States Patent Carothers et al.

[54] ELECTRICAL DISCONNECTOR [72] Inventors: Charles H. Carothers;Robert M. Kelly,

both of Bloomington, 1nd.

Westinghouse Electric Corporation, Pittsburgh, Pa.

22 Filed: Sept. 29, 1970 211 Appl.No.: 76,573

[73] Assignee:

[ 1 July 25, 1972 Attorney-A. T. Stratton, F. P. Lyle and Gordon H.Telfer 57 ABSTRACT A disconnector for lightning arresters is providedwith a simplified configuration wherein a cup-shaped breakable housinghas within it a substantially concentric insulating support member thatis recessed to accommodate an explosive containing metal case resting onan end portion of a ground terminal. The insulating support defines afixed spark gap spacing between the metal case and an electrode makingdirect contact with a lightning arrester. A flexible grading resistor isprovided in parallel with the spark gap and comprises a flexibleinsulating core on which is wound a plurality of turns of resistivewire, the resistor encircling the insulating support in the spacebetween it and the inner housing wall.

6 Claims, 3 Drawing Figures PATENTEDJUL25I97Z 3.679.938

FIGI.

INVENTORS Charles H. Coro'rhers&

Robert M. Kelly.

BY QM @551 ATTORNEY BACKGROUND OF THE INVENTION 1. Field of theInvention The invention relates to explosive circuit opening devices(sometimes called disconnectors) for excess voltage protection devicessuch as lightning arresters.

2. Prior Art Disconnectors are known types of electrical devices used inassociation with devices such as lightning arresters. When the arresteris subjected to a current surge beyond its capabilities to extinguish,or is damaged internally from some other abnormal condition; anexplosive element in the disconnector is detonated to remove the groundlead from the arrester while some system backup device is clearing thecircuit.

Continuing efforts are made to design disconnectors that are simpler,easier to make, hence less expensive, without detracting from theirelectrical functions. One example of the prior art on which the presentinvention improves is copending application Ser. No. 816,538, filed Apr.16, 1969, now Pat. No. 3,588,733, by C. H. Corothers and assigned to thepresent assignee.

The explosive element in a disconnector is detonated by reason ofcurrent crossing a spark gap between the metal explosive-containing caseand another element. It has been recognized previously that there areadvantages in having another electrical path parallel to the spark gapof some substantial resistance, for example 500 ohms, to carry thenormal arrester grading current and to carry external leakage currentsthat may be created by contaminants on the housing so as to avoid radionoise occurring by minor discharges at the spark gap and to assist inthe controlled functioning of the lightning arrester and disconnector.

The above-mentioned application provided a leakage-current resistor inthe form of a simple carbon resistor secured across the spark gap. Sucha resistor offers the advantage of economy. However, such carbonresistors are limited in power dissipation and, hence, in the amount ofleakage current which they can sustain. Other types of resistors havealso been used in disconnectors yet not without the difficulties ofproviding an optimum combination of economy and functional capability.

SUMMARY OF THE INVENTION The present invention provides a structurallysimplified disconnector that permits use of an economical resistorelement that provides all of the required electrical characteristics.Briefly, a disconnector in accordance with the present inventioncomprises a cup-shaped breakable housing having a rim for securing to anexcess-voltage protective device and a center bore through which aground terminal member extends. A support member of insulating materialis disposed within the housing and has a recess accommodating anexplosive-containing metal case in a manner that the metal case is indirect electrical contact with the end portion of the ground terminaland also provides a predetermined spacing between the metal case andanother electrode to define the operative spark gap of the device.Connected in parallel across the spark gap is a resistor that comprisesa flexible insulating core on which are wound a plurality of turns ofresistive wire, such resistor encircling the support member for asubstantial portion of the circumference. Such a resistor, commerciallyavailable and known as a flexible grading resistor, provides not onlythe desired electrical characteristics in terms of ohmic value and powerdissipation but also permits a convenient arrangement wherein theinsulating support member may be substantially concentrically arrangedwithin the cup-shaped housing with a gap therebetween in which thegrading resistor is disposed.

Among other advantages provided by preferred forms of the presentinvention are that the insulating support member, explosive-containingmetal case, resistor and other elements may be formed in a sub-assemblyseparate from the cupshaped housing to facilitate overall assemblyoperations and permit resistor continuity and gap spacing electricaltests to be made prior to completion of the unit. Furthermore, inaccordance with this invention, an additional advantage is provided inthat the spark gap to the metal case is to the shank portion proximateto the center of mass of the explosive contained therein resulting infaster operating time and higher reliablity in firing the explosive.Also, since the metal mass is greater in the shank than in the head ofthe cartridge there is considerably less erosion due to arcing in normalarrester operations.

THE DRAWING FIG. 1 is a sectional view of a disconnector device inaccordance with the present invention;

FIG. 2 is a plan elevation view, partly broken away, looking upward, ofa portion of the device shown in FIG. 1; and

FIG. 3 is a plan elevational view looking down on a portion of thedevice of FIG. 1.

DESCRIPTION Referring now to the drawing, particularly FIG. 1 thereof, adisconnector in accordance with this invention is shown that includes acup-shaped breakable housing 10, such as of some fracturable insulatingmaterial. The housing has a rim 12 for securing to an excess voltageprotective device 14 such as a lightning arrester. The lightningarrester 14 includes a conductive end member 15 directly joined to therim [2 of the housing. At the bottom of the housing 10 is a groundterminal member 16 which has a threaded stud portion 17 extendingthrough a center bore 11 of the housing and also has an end portion 18that is generally flat and is disposed within a recess 13 in the bottomof the housing interior. A nut 20 on the threaded stud 17 providessecure attachment of the ground terminal and the housing in a mannerthat avoids contaminants inside the housing such as by a gasket seal 22occurring at the edge of the center bore 11 between a shoulder of thehousing and the end portion 18 of the ground terminal.

FIG. 3 shows a view looking into the housing 10 from its upper rim l2and showing the ground terminal 16 in its position, but without anyother elements in the housing. The ground terminal 16 has somestructural configuration on top of the otherwise flat surface of endportion 18 as will be subsequently described for support of additionalelements of the device.

Referring back to FIG. 1, within the housing 10 and supported on the endportion 18 of the ground terminal 16 is an insulating support member 24that may be of some molded insulating material and has within its lowerface, also shown in FIG. 2, a recess 26 accommodating an explosiveisolator device, 28, that is, an explosive containing metal case orcartridge. The insulating support member 24 preferably has an outersurface 27 that is substantially cylindrical and concentric with asubstantially cylindrical inner surface 37 of the housing 10 with someappreciable space therebetween. The insulating support member 24 has itsrecess 26 configured to fit over an embossed portion 19 of the end ofthe ground terminal so that the cartridge 28 rests in a depression 30 inthe embossed portion and its head portion 29 is disposed within a recess31 in the end of the ground terminal.

The cartridge 28 is thus in direct electrical contact with the groundterminal 16. The insulating support 24 also includes a portion 32 (FIG.1)that defines a predetermined spacing for a spark gap 33 between thecartridge 28 and an electrode 34, that may be in the form of a rivet asshown, that is secured into the upper portion of the insulating support.The rivet electrode 34 makes electrical contact with the end 15 of thelightning arrester by some sort of spring contact 36 which may be a leafspring as shown or a coil spring.

Means are provided to form two electrical paths between the face 15 ofthe lightning arrester and the ground terminal 16. A first electricalpath in this embodiment is one that passes from the lightning arresterthrough the spring contact 36, the

rivet electrode 34, across the spark gap 33 to the shank of theexplosive cartridge 28 and through the ground terminal l6. The explosivecartridge 28 is an elongated member as is normally used in disconnectorsbut in this invention it is disposed with its long dimension parallel tothe base of the disconnector rather than extending in line with theground stud. This arrangement makes the spark occur directly to theportion of the cartridge associated with the greater mass of explosivematerial to result in prompt, reliable firing. Other arrangements inwhich the spark gap is made to the head of the cartridge have been foundto operate in a longer time and generally more unreliably, one reasonbeing because of greater erosion of the metal from the edge of the headof the cartridge as compared with the shank portion, as well as thegreater distance from the center of mass of the explosive.

The second electrical path in the device is provided through a resistor38 that is electrically in parallel with the spark gap 33. The resistor38 is connected by spring contacts 39 and 40 at its ends. One springcontact 39 is joined to one end of the resistor at the side of the upperportion of the insulating housing and is in contact with contact 36. Theother spring contact 40 extends under the edge of the insulating supportmember 24 and makes contact to the head 29 of the explosive cartridge28.

The resistor 38 is, in accordance with one aspect of this invention, aflexible grading resistor, that is, one that comprises a flexibleinsulating core 42 (FIG. 2) on which are wound a plurality of turns 44of fine resistive wire such as of Nichrome alloy. After the resistor 38is wound, there may be an insulating coating 46 applied over the turnsfor protection thereof. Such flexible grading resistors are known per seand have found application of the past in automotive voltage regulators,for example. Here advantage is taken of the fact that the flexibility ofthe resistor 38 permits it to be wound around the insulating support,substantially encircling it. For whatever portion of its length isnecessary, a flexible conductor 48 may be provided. Thus the length ofthe resistor 38 does not impose undue space requirements on thedisconnector device. In fact, if an equivalent resistor were to beprovided by rigid material it would require substantially more size.Furthermore, the flexible grading resistor 38 is one that has greaterpower dissipating capability than. a carbon resistor, as in theabove-mentioned copending application, and can thereby withstand a 100milliampere leakage current which could be encountered in areas withsevere atmospheric contamination. There are commercially available suchresistors of suitable ohmic value, such as 500 ohms, suitableflexibility and power dissipation of about 8 watts as compared to onlyone-half watt with carbon resistors of similar price. The flexibleresistor 38 can be easily formed to fit the contour of the molded cup,thereby occupying a minimum of space and necessitating little increasein the size of the disconnector cup. In fact, as compared with theembodiment of the described copending application, the outside diameterof the cup has been maintained. Thus the method of attaching thedisconnector to the arrester is the same as before. The use of a rigidresistor of the required resistance and power dissipating capabilitywould necessitate a much larger cup and would cost about five times theprice of the flexible resistor in accordance with this invention.Attachment of the resistor 38 to the spring contacts 39 and 40 such asby a spot weld provides sufficient mechanical strength to allowconstruction of a sub-assembly of all the internal parts on theinsulating support member, as shown in FIG. 2, separate from the cup 10and ground terminal 16. Such a sub-assembly fabricated outside themolded cup facilitates assembly and allows resistor continuity and gapspacing electrical tests to be made prior to completion of the unit.

The cylindrical wall of the housing provides increased torque strength.For example, in embodiments that have been made torque strength has beenfound to be in a range of 40 to 45 ft. lbs. as compared to 30 to 35 ft.lbs. for similar sized items in accordance with thecopendingapplication. Also the stud supporting surface is inside the cupeliminating the possibility of the stud being pulled loose from thedisconnector. The screw-on nut 20 insures a weather-tight seal and addsstrength to the bottom portion of the molded cup by placing the materialin compression.

We claim:

1. An explosive circuit-opening device comprising: a cupshaped breakablehousing having a rim for securing to an excess-voltage protective deviceand a center bore through which a ground terminal member extends; saidground terminal member having an end portion within said housing, aunitary support member of insulating material having a recessaccommodating an explosive-containing metal case, said insulatingsupport member being disposed on said end portion of said groundterminal with said metal case being in direct electrical contact withsaid end portion; an electrode member within a portion of saidinsulating support member and spaced a predetermined distance from saidmetal case and defining the operative spark gap of said devicetherebetween.

2. The subject matter of claim 1 wherein: a resistor is connected toprovide an electrical path in parallel with said spark gap, saidr'esistor comprising a flexible insulating core on which are wound aplurality of turns of resistive wire, said resistor encircling saidsupport member for a substantial portion of its circumference.

3. The subject matter of claim 2, wherein: said housing has asubstantially cylindrical inner surface; said insulating support memberhas a substantially cylindrical outer surface that is substantiallyconcentric with said inner surface of said housing with a spacetherebetween.

4. The subject matter of claim 3 wherein a first spring contact makeselectrical contact between one end of said resistor and said metal caseand a second spring contact makes electrical contact between saidelectrode and theother end of said resistor.

5. The subject matter of claim 1 wherein: said end portion of saidground terminal is a generally flat portion resting within a recess inthe bottom surface of the inside of said housing.

6. The subject matter of claim 5 wherein: said explosivecontaining metalcase has an elongated configuration with its long dimensionsubstantially parallel with said end portion of said ground terminal.

1. An explosive circuit-opening device comprising: a cup-shapedbreakable housing having a rim for securing to an excess-voltageprotective device and a center bore through which a ground terminalmember extends; said ground terminal member having an end portion withinsaid housing, a unitary support member of insulating material having arecess accommodating an explosivecontaining metal case, said insulatingsupport member being disposed on said end portion of said groundterminal with said metal case being in direct electrical contact withsaid end portion; an electrode member within a portion of saidinsulating support member and spaced a predetermined distance from saidmetal case and defining the operative spark gap of said devicetherebetween.
 2. The subject matter of claim 1 wherein: a resistor isconnected to provide an electrical path in parallel with said spark gap,said resistor comprising a flexible insulating core on which are wound aplurality of turns of resistive wire, said resistor encircling saidsupport member for a substantial portion of its circumference.
 3. Thesubject matter of claim 2, wherein: said housing has a substantiallycylindrical inner surface; said insulating support member has asubstantially cylindrical outer surface that is substantially concentricwith said inner surface of said housing with a space therebetween. 4.The subject matter of claim 3 wherein a first spring contact makeselectrical contact between one end of said resistor and said metal caseand a second spring contact makes electrical contact between saidelectrode and the other end of said resistor.
 5. The subject matter ofclaim 1 wherein: said end portion of said ground terminal is a generallyflat portion resting within a recess in the bottom surface of the insideof said housing.
 6. The subject matter of claim 5 wherein: saidexplosive-containing metal case has an elongated configuration with itslong dimension substantially parallel with said end portion of saidground terminal.